Device for filtering fluids containing impurities

ABSTRACT

A filter apparatus for liquids containing impurities, in particular solid particles, preferably for filtering plasticized thermoplastic synthetic plastic material, has a housing ( 1 ) in which at least one stationary, substantially flat filter ( 5 ) is disposed. The liquid to be cleaned is supplied to the filter ( 5 ) in the region of its periphery through at least one supply channel ( 3 ). The cleaned liquid is conducted off the housing through at least one downstream channel ( 7 ). At least one scraper element ( 17 ) is pressed with its scraping edge ( 31 ) against the upstream-side surface ( 11 ) of the filter ( 5 ), this scraper element ( 17 ) being movably connected to a scraper carrier ( 12 ) which can be rotated by a drive means ( 15 ) around an axis which is directed substantially perpendicular to the upstream-side surface ( 11 ) of the filter ( 5 ). The scraper element ( 17 ) strips off the impurities adhering to this surface ( 11 ) and conveys them towards the center of the filter ( 5 ) wherefrom the impurities are conveyed off the housing by means of at least one screw ( 38 ) through at least one discharge channel ( 39 ) starting from the center of the filter ( 5 ) and extending out of the housing ( 1 ). At least one scraper element ( 17 ) is connected to the scraper carrier ( 12 ) so that it can swivel around an axis ( 18 ) and the scraper element ( 17 ) extends from this axis obliquely with respect to the filter ( 5 ) in direction of rotation of the scraper carrier ( 12 ). The scraping edge ( 31 ) of the scraper element ( 17 ) is pressed by the counter-pressure of the liquid to be cleaned against the filter ( 5 ), when the scraper carrier ( 12 ) is in rotation. Thereby, a blocking of the scraper element ( 17 ) is effectively avoided.

TECHNICAL FIELD

The invention relates to a filter apparatus for liquids containingimpurities, in particular solid particles, and more particularly to afilter apparatus for filtering plasticised thermoplastic syntheticplastic material, comprising a housing in which there is disposed atleast one stationary, substantially flat filter to which the liquid tobe cleaned is supplied in the region of its periphery by means of atleast one supply channel, and from which the cleaned fluid is conductedoff and out of the housing through at least one downstream channel, andfurther comprising at least one scraper element which has a scrapingedge that is pressed against the upstream side surface of the filter andis movably connected to a scraper carrier which can be rotated by adrive means around an axis disposed substantially perpendicular to theupstream-side surface of the filter, whereby the scraper element stripsoff the impurities adhering to this surface and conveys them towards thecenter of filter, wherefrom the impurities are conveyed off the housingby means of at least one screw through at least one discharge channelstarting from the center of the filter and extending out of the housing.

BACKGROUND OF RELATED ART

Such a filter apparatus is known (WO 94/17981). Within this knownapparatus, each one of the scraping edges is constituted by a pluralityof scraper elements separated from each other and pressed against thefilter either by means of springs or by means of the pressure of thesupplied liquid to be filtered. In the latter case, the scraper elementsare movably connected to the scraper carrier by means of pins directedperpendicular to the filter surface so that each element can move alongthe pins, and each scraper element is so designed that the pressureexerted on it by the supplied liquid in direction towards the filter isgreater than the pressure acting in the opposite direction. Bothembodiments, however, suffer from the disadvantage that a solid particlecan adhere between the filter and the scraper element, so that it is notengaged by the scraping edge of the scraper element. Then, this solidparticle keeps the scraper element spaced apart from the filter surfaceto be cleaned so that the respective scraper element becomes inactive.This leads not only to a decrease of the cleaning effect on theupstream-side filter surface, but frequently causes also an additionalwear on this surface by solid particles conveyed always along a circleand having frequently sharp edges.

SUMMARY

The invention has at its object to avoid this disadvantage of the knownapparatus in a simple manner. The invention solves this task by the factthat at least one scraper element is mounted on the scraper carrierswivellable around an axis and protudes from this axis towards thefilter obliquely and in direction of motion of the scraper carrier, thescraping edge of the scraper element being pressed towards the filterduring revolution of the scraper element by the counter-pressure of theliquid to be cleaned. Therefore, the respective scraper element is somounted on the scraper carrier that it can freely oscillate or swing,however, it protudes from the scraper carrier in direction of itsrotation. As soon as the revolution of the scraper carrier around itsaxis of revolution is started, the counter-pressure exerted onto thescraper element by the fluid to be cleaned presses this scraper elementagainst the filter surface to be cleaned so that there an effectivescraping action occurs. There are no dead spaces in which solidparticles can rest, so that there are no particles hindering thisfunction of the scraper element, so that always a reliable function ofthe scraper element is ensured, if the construction is suitably made.

According to a preferred embodiment of the invention, the scraperelement has a straight-lined scraping edge extending parallel to theswivel axis, the outer end of the scraping edge advances or leadsrelative to a radial line starting from the axis of rotation of thescraper carrier and extending to the inner end of the scraping edge,when seen in direction of revolution of the scraper carrier. By thisdisposition of the swivel axis of the scraper element and its scrapingedge a conveyance of the impurities scraped off the filter surface to becleaned towards the center of the filter is automatically obtained, whenthe scraper carrier rotates, and these impuritites are taken up by atleast one screw and are conveyed off the housing through the dischargechannel.

As a rule, a plurality of scraper elements are swivelably connected tothe scraper carrier in the described manner, and these scraper elementsare arranged star-shaped with respect to the axis of revolution of thescraper carrier. However, always two or more scraper elements can bedisposed along an arm of such a star so that their scraping edgesconstitute extensions with respect to each other, e.g. along curvedpaths, as this is the case within scraper elements of the initiallydescribed known apparatus. As a rule, however, one single scraperelement per said arm of the star is sufficient. In order to ensure thatthe impurities scraped off by the scraper element are reliably conveyedtowards the center of the filter element, according to a furtherembodiment of the invention a protrusion on the scraper carrier may beprovided adjacent to the inner end of the scraping edge of the scraperelement which protrusion is directed towards the center region of thescraper carrier and conveys the impurities towards the center of thefilter and to the discharge channel. Preferably, within the spirit ofthe invention, this protrusion is formed as a ledge extending with itslongitudinal extension in direction of the scraping edge of the scraperelement.

According to a suitable further embodiment of the invention, the scraperelement carries a wearing member which constitutes the scraping edge andpreferably is exchangeable. As soon as a wear occurs at this wearingmember, this wearing member is exchanged so that an effective functionis obtained again.

A particular favourable embodiment of the inventions consists in thatthe supply channel is conducted into a space between two adjacentfilters which preferably are disposed in parallel to each other, thescraper carrier being common for both filters and carries on its bothsides scraper elements cooperating with the filters, which scraperelements preferably are disposed in pairs, each of which scraperelements carries on its end facing the filter a member constituting thescraping edge, preferably a wearing member, which member has twoscraping edges and the scraper elements of the one side of the scrapercarrier are exchangeable against the scraper elements of the other sideof the scraper carrier. Thereby, the working life time of each scraperelement or, respectively, of its wearing member can be doubled.

A further improvement of the filter action can be obtained according toa further embodiment of the invention by the fact that at least onesupply channel leads to a distribution space which surrounds the filteror the filters along at least of a major part of its periphery or theirperiphery, respectively, which distribution space is in connection via aplurality of openings provided in an intermediate wall with theupstream-side of the filter or, respectively, with the space disposedbetween the two filters. The distribution space ensures that the filtersurface over at least the major part of its periphery, if desired evenover the entire periphery, is supplied with the liquid to be cleaned.The openings in the intermediate wall constitute a preliminary filterwhich retains coarse impurities, e.g. metal clips, stones and the like.Thereby, the real filter is relieved and treated with care.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention can be seen from thedescription of examplative embodiments of the subject matter of theinvention, which embodiments are schematically shown in the drawings.

FIG. 1 shows a vertical section through a filter apparatus.

FIG. 2 shows a view of the scraper carrier, seen in direction of theaxis of its rotation.

FIG. 3 is a top view to FIG. 2 in direction of the arrow III.

FIG. 4 shows a detail in a section taken along the line IV—IV of FIG. 2in an enlarged scale.

FIG. 5 shows the cooperation of two scraper elements with the adjacentfilter surfaces.

FIG. 6 shows a variant to FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

The filter apparatus according to FIG. 1 has a housing 1 into which theliquid impured by solid particles, in particular soiled thermoplasticplasticised synthetic material, is introduced into a supply channel 3 indirection of the arrow 2. This supply channel 3 leads to an annularspace 4 which is provided between two parallelly disposed stationaryfilters 5, each of which being substantially flat. Preferably, each oneof these filters 5 comprises a filter plate provided with fine holeswhich, preferably, are bored by means of electron beams or laser beams,whereby this filter plate is abutted on its downstream side by a supportplate, the penetration bores of which having a substantially greaterdiameter than the fine holes of the filter plate. This enables to loadthe filter by high pressures, e.g. about 300 bar and more, of thesupplied fluid to be cleaned. The filters 5 or, respectively, the platesof each filter structure are flat, however, they may slightly differfrom the complete flat form, in particular, they may be slightlycone-shaped. A plurality of supply channels 3 may lead into the space 4between the two filters 5.

Collection spaces 6 are disposed on the downstream side of each filter 5and each collection space 6 leads to a downstream channel 7 throughwhich the cleaned fluid flows off the housing 1 in direction of thearrow 8. A plurality of downstream channels 7 may be provided. Eachdownstream channel 7 as well as each supply channel 3 is disposed in theregion of the outer pheriphery of the two ring disks constituting thetwo filters 5.

The two filters 5 are secured within the housing 1 against rotation andare sealingly fixed on their outer periphery 9 by means of annularmountings 10 so that any bent of the filters 5 can be taken up which mayoccur due to the high pressure of the material to be filtered.Simultaneously, these mountings 10 constitute sealing means for thespace 4 so that no material to be filtered may reach the downstreamchannel 7 by by-passing the filter 5.

The impurities of the supplied liquid which cannot pass the fineopenings of the filter 5, gather at the upstream-side surface 11 of thefilter 5 and are scraped off there. For this, a disk-shaped scrapercarrier 12 is disposed between the two filters 5 and this scrapercarrier is connected in its center region for common rotation with ashaft 13, the axis 14 of which is directed perpendicular to the plane ofeach one of the filters 5, this axis simultaneously constituting theaxis of rotation of the scraper carrier 12. This shaft 13 is connectedto a drive means 15 for continuous rotation around its axis 14, thisdrive means 15 being only schematically shown. The scraper carrier 12carries on each one of its two surfaces 16, each one of which faces therespective filter 5, a plurality of scraper elements 17 which aredisposed in equal distances from each other along the periphery of thescraper carrier 12. Each one of these scraper elements 17 is mounted onthe scraper carrier 12 swivellably around an axis 18 (FIGS. 2, 4, 5),which axis in the embodiment shown is formed by a round profile member19 composed of two rods each of one having a semicircular cross section,the two rods being disposed mirror-inverted, and a plate 21 is insertedinto the space 20 between the two semi-circular rods, which plate 21constitutes the base body of the scraper element 17 and is connectedloosely to the two semi-circular rods by means of pins 22 extendingperpendicular to the plane of the plate 21, however, the plate 21 beingsecured against being drawn off the semi-circular rods. One single rodhaving a circular cross section and being slotted may replace the twosemi-circular rods, the plate 21 being inserted into this slot and beingsecured against pulling off by the pins 22 or by means of screws. Theswivelling range of each scraper element 17 around the axis of therounded profile member 19 is limited by the fact that the roundedprofile member over the major part of its periphery is covered by thematerial of the scraper carrier 12, whereby the regions 23 of thescraper carrier 12 which embrace the rounded profile member 19constitute limiting stops for the swivelling range of the plate 21. Eachrounded profile member 19 is secured against falling out of the scrapercarrier 12, e.g. by inserting the rounded profile member into a blindbore 24 (FIG. 2), the open end of this bore being closed by a closuremember 25 screwed to the scraper carrier 12.

Each plate 21 of the scraper element 17 carries on its free end awearing member 26 exchangeably connected to the plate 17. For this, eachwearing member 26 has the shape of a ledge and has a longitudinal slot27 by which it is pinned up to the plate 21 of the scraper element 17. Ascrew 29 screwed into a transverse bore 28 of the plate 21 secures thewearing member 26 against pulling off the plate 21. The screw 29 isinserted with play into a bore 30 having a greater diameter than thescrew 29, so that the screw 29 enters the bore 30 with a clearance sothat the wearing member 26 can be slightly moved in direction of theplane of the plate 21. Therefore, the wearing member 26 can follow thebents of the filters 5. Further, thereby inaccuracies of the manufactureare taken up in an easy manner, what is of advantage because the wearingmembers 26 which as a rule constitute of hard metal, which allows anafter treatment only very hard. Each wearing member 26 has two scrapingedges 31, always one of which scraping the impurities off theupstream-side surface 11 of the neighbouring filter 5 and carries themtowards the region 32 of the center of the scraper carrier 12. This isensured on the one hand by rotating the scraper carrier 12 around theaxis 14 by means of drive means 15, and on the other hand by directingthe scraping edges 31 so that their longitudinal direction extends pastthe axis 14 (that is identical to the center 33 of the scraper carrier12 or, respectively, of the two filters 5), so that the outer end 34 ofeach scraping edge 31 advances relative to a radial direction extendingfrom the axis 14 of the scraper carrier 12 and leading through the innerend 35 of the scraping edge 31. Following each wearing member 26, thedisk constituting the body member 36 of the scraper carrier 12 carriesalways a protrusion 37 which protrusions—as to say—form extensions ofthe scraper edges 31 and convey the impurities scraped off towards thecenter region 32 of the scraper carrier 12. In this region, theimpurities are taken up by two screws 38 starting from the two sides ofthe scraper carrier 12 and extending in opposite directions, and havingscrew threads machined into the surface of the shaft 13, the screws 38being bearingly supported within discharge channels 39 through which theimpurities are conveyed by the screws 38 towards openings 40 throughwhich the impurities leave the respective housing 42 of the screw 38 indirection of arrows 41. The outer end of each shaft 13 is provided withscrew threads 43 behind the opening 40, which screw threads areoppositely directed to the direction of the screw threads of the screw38, so that these screw threads 43 act as a sealing.

In the embodiment shown, each protrusion 37 has the shape of a ledge,the longitudinal direction of which extends parallel to the longitudinaldirection of the straight-lined scraping edge 31. However, theprotrusions 31 can also be designed as filler pieces of any desiredshape, e.g. having triangular shape or curved, and if so, the shape ofthe curvature or, respectively, the angle of the bent of this fillerpiece constituting the protrusion is so chosen that the said conveyanceof the impurities towards the center of the scraper carrier 12 isensured. In an analogous manner, the scraping edges 31 must not extendstraight-lined, they may also have a curved or bent or angled shape.

In operation, when the scraper carrier 12 rotates in direction of thearrow 44 (FIG. 5) around its axis 14, the wearing member 26 is pressedwith its outer scraping edge 31 against the upstream-side surface 11 ofthe filter 5 (see also FIG. 5). This pressure is exerted by the counterpressure in direction of the arrows 45 exerted by the liquid to befiltered within the space 4 onto the plates 21, when the scraperelements 17 are advanced. Thus, no springs are necessary in order topress the scraper edges against the filter, so that the apparatus isinsensitive to spring fracture. Further, this pressing is alsosubstantially independent from the pressure of the fluid to be filteredwithin the space 4, so that the apparatus can be used for any pressureof the material to be filtered. However, the said pressing of thescraper element 17 against the filter surface 11 is dependent from therotational speed of the scraper carrier 12 within the space 4 and fromthe viscosity of the liquid to be filtered so that there is thepossibility to adjust the desired pressure by which the scraper elements17 are pressed onto the filter surface 11 by selection of thisrotational speed, or, respectively, to adapt the operation to theviscosity of the liquid to be filtered. The function of the scraperelements 17 cannot be detrimentally influenced or blocked by solidparticles squeezed between the scraper elements 17 and the filtersurface 11.

The arrangement of two filters 5 in parallel has not only the advantageof an increase of the active filter surface and thereby of an increaseof the throughput of the filter apparatus, but also the advantage thatthe scraper elements 17 cooperating with the one filter 5 can beexchanged against the scraper elements cooperating with the other filter5, so that thereby an exchange of the respective active scraping edge 31of each scraper element 17 can be obtained. For this, only the screwsfixing the closure member 25 must be loosened and the scraper elements17 with their rounded profiles 19 must be pulled off the respectivebores 24, and then, the scraper elements 17 must be exchanged in thedescribed manner and the rounded profiles 19 must be inserted again intothe bores 24 and secured by means of the closure members 25, whereuponthe apparatus is ready for operation again.

In order to enable mounting and dismounting, the housing 1 is composedof two parts and also the shaft 13 is composed of two parts, the twoshaft parts being connected to each other for common rotation by apositive connection 46 (FIG. 1), e.g. by means of a hexagon connectionor a toothed connection, so that both shaft parts can be driven forrotation in common by the drive means 15. The scraper carrier 12 isinserted into a step 49 of the two sections of the shaft 13 and isconnected thereto for common rotation in the same manner as the twoparts of the shaft. This construction is held together by a screw 50,the outer threads of which are screwed into inner threads 51 of the lefthand shaft part, which screw intersects a bore 52 of the right hand ashaft part and is abutted with its head 53 to this shaft part.

If desired, the ledge-shaped protusions 37 may have interruptions 47(FIG. 2), in order to give more room for the screws 48 by which thefilters 5 are screwed to the housing 1.

The embodiment according to FIG. 6 differs from that according to FIG. 1in that the mounting 10 for the two filters 5 is an annular intermediatewall 54 which is perforated along its periphery by a plurality ofopenings 55. This intermediate wall 54 confines together with thehousing 1 an annular distribution space 56 which is in flow connectionwith the supply channel 3 or the supply channels and surrounds thefilters 5 along their outer peripheries and via the openings 55 is inflow connection with the space 4 so that the upstream-side surfaces 11of the filters 5 are equally supplied with liquid to be filtered.Simultaneously, the intermediate wall 54 with its openings 55constitutes a pre-filter which retains coarse impurities introduced bythe liquid to be cleaned via the supply channels 3 into the distributionspace 56.

What is claimed is:
 1. Filter apparatus for liquids containingimpurities, in the form of solid particles comprising: a housing inwhich at least one stationary, substantially flat filter is disposed towhich the liquid to be cleaned is supplied in the region of itsperiphery via at least one supply channel and from which the cleanedfluid is conducted off the housing via at least one downstream channel,at least one scraper element, having a scraping edge that is pressedagainst the upstream-side surface of the filter and is movably connectedto a scraper carrier that is rotatable around an axis disposedsubstantially perpendicular to the upstream-side surface of the filterby a drive means, the scraper element scraping off the impuritiesadhering to this surface and conveying them towards the center of thefilter, wherefrom the impurities are conveyed off the housing by meansof at least one screw via at least one discharge channel that startsfrom the center of the filter and conducts the impurities out of thehousing, wherein at least one scraper element is connected to thescraper carrier swivellably around an axis and extending from this axisin the direction of rotation of the scraper carrier and obliquely to thefilter, the scraping edge of the scraper element being pressed againstthe filter during revolution of the scraper element by thecounter-pressure of the liquid to be cleaned.
 2. Filter apparatusaccording to claim 1, wherein the scraper element has at least onestraight-line scraping edge disposed in parallel to the swivel axis, theouter end of the scraping edge advances relative to a radial linestarting from the axis of rotation of the scraper carrier and extendingto the inner end of the scraping edge, when seen in direction ofrevolution of the scraper carrier.
 3. Filter apparatus according toclaim 1, wherein a protrusion is provided on the scraper carrieradjacent to the inner end of the scraping edge, which protrusion isdirected towards the center region of the scraper carrier and conveysthe impurities towards the center of the filter.
 4. Filter apparatusaccording to claim 3, wherein the protrusion is a ledge extending withits longitudinal direction in longitudinal direction of the scrapingedge of the scraper element.
 5. Filter apparatus according to claim 1,wherein the scraper element comprises a plate connected on its edge to arounded profile member, which rounded profile member is inserted into amatching bore of the scraper carrier so that a swivel bearing for theplate is formed.
 6. Filter apparatus according to claim 5, wherein theregions of the scraper carrier which embrace the rounded profile memberconstitute stop limits for the swivel region of the scraper element. 7.Filter apparatus according to claim 5, wherein the rounded profilemember is formed by a rod having a circular cross section, which rod isconnected by means of transversely extending screws or pins to the plateand is secured against falling out of the bore.
 8. Filter apparatusaccording to claim 1, wherein the scraper element carries a wearingmember constituting the scraping edge.
 9. Filter apparatus according toclaim 1, wherein the supply channel leads into a space between twoadjacent filters, the scraper carrier being common for both filters andcarries on both of its sides scraper elements cooperating with thefilters, each one of these scraper elements carries on its end facingthe filter a member constituting the scraping edge, which membercomprises two scraping edges, the scraper elements of the one side ofthe scraper carrier being exchangeable against the scraper elements ofthe other side of the scraper carrier.
 10. Filter apparatus according toclaim 1, wherein at least one supply channel leads to a distributionspace which surrounds the filter or the filters over at least a majorpart of the periphery and is in flow connection via a plurality ofopenings in an intermediate wall with the upstream-side surface of thefilter.
 11. Filter apparatus according to claim 10, wherein the openingsconstitute a pre-filter for coarse impurities.
 12. Filter apparatusaccording to claim 10, wherein the annular intermediate wall constitutesa mounting for the filters.
 13. Filter apparatus according to claim 1,wherein the liquid being filtered comprises a plasticized thermoplasticsynthetic plastics material.
 14. Filter apparatus according to claim 1,wherein the scraper element comprises a plate formed as a unitarystructure with a rounded profile member, which rounded profile member isinserted into a matching bore of the scraper carrier so that a swivelbearing for the plate is formed.
 15. Filter apparatus according to claim5, wherein the rounded profile member is formed by two rods each onehaving a semicircular cross section, which rods are connected by meansof transversely extending screws or pins to the plate and are securedagainst falling out of the bore.
 16. Filter apparatus according to claim15, wherein the rods are secured against falling out of the bore by aclosure member closing the end of the bore and screwed to the scrapercarrier.
 17. Filter apparatus according to claim 7, wherein the rod issecured against falling out of the bore by a closure member closing theend of the bore and screwed to the scraper carrier.
 18. Filter apparatusaccording to claim 8, wherein the wearing member is an exchangeablemember.
 19. Filter apparatus according to claim 9, wherein the twoadjacent filters are disposed parallel to each other.
 20. Filterapparatus according to claim 9, wherein the scraper elements comprise apair of scraper elements.
 21. Filter apparatus according to claim 9,wherein the member carried on the scraper elements on the end facing thefilter is a wearing member.
 22. Filter apparatus according to claim 1,wherein at least one supply channel leads to a distribution space whichsurrounds the filter or the filters over at least a major part of theperiphery and is in flow connection via a plurality of openings in anintermediate wall with the space being disposed between the two filters.